Concrete is one of most extensively used construction materials in the world with two billion tons placed worldwide each year . It is attractive in many applications because it offers considerable strength at a relatively low cost. Concrete cangenerally be produced of locally available constituents, can be castinto a wide variety of structural configurations and requires minimal maintenance during service. However, environmental concerns, stemming from the high energy expense and CO2 emission associated with cement manufacture have brought about pressures to reduce cement consumption through the use of supplementary materials
Supplementary cementitious materials (SCMs) are finely ground solid materials that are used to replace part of the cement in a concrete mixture. These materials react chemically with hydrating cement to form a modified paste micro structure. In addition to their positive environmental impact, SCMs may improve concrete workability, mechanical properties, and durability. SCMs may possess pozzolanic or latent hydraulic reactivity or a combination of these.The term pozzolan refers to a silecious material, which, in finely divided form and in the presence of water, will react chemically with calcium hydroxide (CH1) to form cementitious compounds.Pozzolans can be of natural or industrial origin.
kaolin for coating
kaolin for coatings
KAOLIN FOR RUBBER
KAOLIN FOR Paper
Metakaolin is an SCM that conforms to ASTM C618, Class N pozzolan specifications. POZZOFILZ HRM is unique in that it is not the by-product of an industrial process nor is itentirely natural; it is derived from a naturally occurring mineraland is manufactured specifically for cementing applications. Unlikeby-product pozzolans, which can have variable composition, POZZOFILZ HRM is produced under carefully controlled conditions to refine itscolor, remove inert impurities, and tailor particle size such, amuch higher degree of purity and pozzolanic reactivity can be obtained. POZZOFILZ HRM has great promise as an SCM, as it can improve many properties of concrete while also reducing cement consumption.
Regardless of the reactivity of an SCM, if it is extremely fine, itwill generally impart some benefit to mortars and concrete. Small particles, which can fit between cement grains, allow for more efficient paste packing, which in turn reduces bleeding, lowers the mean size of capillary pores, and may reduce water requirement
Another important factor to consider when using SCMs is dilution.When used as a replacement for cement, concrete mixtures will experience some effect of the removal of cement from the reacting system. As such, unless the SCM begins reacting immediately, there will generally be a reduction in the rate of heat evolution and strength gain in proportion to the amount of cement being replaced.Fly ash, especially, and even silica fume to a lesser extent, do not show beneficial effects until later in the hydration process
Metakaolin, however, because it is very small and possesses some latent hydraulic reactivity, may overcome the dilution effect, contributing to both heat and strength evolution at very early ages.
Metakaolin is a proven alternative to Silica Fume. From elegant interior concrete fixtures, to large High Performance Concrete infrastructure projects, Metakaolin has exceeded the design and performance criteria demanded by architects and engineers.
Metakaolin provides superior pozzolanic performance that contributes to the improved strength, durability, chemical resistance, ASR mitigation, water absorption, efflorescence control,and aesthetics of quality concrete and cement based materials.Metakaolin will also enhance the concrete rheology,providing a smoother, creamier mix that improves the handling and finishing characteristics of the concrete.
History of Pozzolan
Concrete is a compound material made from sand, gravel and cement. The cement is a mixture of various minerals which when mixed with water, hydrate and rapidly become hard binding the sand and gravel into a solid mass. The oldest known surviving concrete is to be found in the former Yugoslavia and was thought to have been laid in 5,600 BC using red lime as the cement.
The first major concrete users were the Egyptians in around 2,500BC and the Romans from 300 BC The Romans found that by mixing a pink sand-like material which they obtained from Pozzuoli with the informal lime-based concretes they obtained a far stronger material.The pink sand turned out to be fine volcanic ash and they had inadvertently produced the first 'pozzolanic' cement. Pozzolana is any siliceous or siliceous and aluminous material which possesses little or no cementitious value in itself but will, if finely divided and mixed with water, chemically react with calcium hydroxide to form compounds with cementitious properties.
The Romans made many developments in concrete technology including the use of lightweight aggregates as in the roof of the Pantheon,and embedded reinforcement in the form of bronze bars, although the difference in thermal expansion between the two materials produced problems of spalling. It is from the Roman words 'caementum' meaninga rough stone or chipping and 'concretus' meaning grown together or compounded, that we have obtained the names for these two now common materials.
Lime and Pozzolana concretes continued to be used intermittently for nearly two millennia before the next major development occurred in 1824 Cement was, made from a mixture of clay and limestone, which had been crushed and fired in a kiln, was an immediate success.Although many developments have since been made, the basic ingredients and processes of manufacture are the same today
The oldest known form of concrete is to be found in the Middle East and it dates back to 5600 BC; the Egyptians (XXVI Century BC) used mixed with straw to bind dried bricks, gypsum and lime mortars in stone masonry (in particular for the construction of pyramids).
The Greeks living in Crete and Cyprus used lime mortars as well(Eight Century BC), whereas Babylonians and Syrians used bitumen to construct stone and brick masonries.
The Ancient Greeks, similarly, used calcined limestone, while the Romans made the first concrete:mixed lime putty with brick dust or volcanic ash. They used it with stone to construct roadways,buildings and aqueducts.
The Romans used pozzolana, a particular type of sand from Pozzuoli,near the volcano Vesuvio (Southern Italy), to construct buildings of crucial importance, such as the Pantheon or the Colosseo.
Pozzolana is an uncommon kind of sand which reacts chemically with lime and water, becoming a rocklike mass; furthermore, it is siliceous and aluminous and it reacts with calcium hydroxide to form compounds with cementation properties.
The domed Pantheon, constructed in the Second Century AD, is one of the structural masterpieces of Roman time: it has a sophisticated structure with a large number of voids, niches and small vaulted spaces aimed at reducing its weight; in particular the dome shows a thicker structure at its base, whereas its thickness tends to diminish gradually, according to the increased height of the dome(in other words, the dome thickness is inversely proportional to its height). Pliny reported a mortar of lime and sand (one part of limeto four parts of sand), and Marco Vitruvio Pollione (First Century BC) reported a mixture of pozzolana and lime (two parts of pozzolanato one part of lime) and we have also an essay of him as regards the properties of concrete.